The subject invention is related to improvements in gaseous ion lasers. It is particularly suited for use in a conduction-cooled laser of the type disclosed in U.S. Pat. Nos. 4,378,600 and 4,376,328, both assigned to the same assignee as the subject invention and incorporated herein by reference.
The type of gaseous ion laser disclosed in the latter patents includes a relatively thin-walled, electrically insulating outer envelope, formed from a ceramic material, such as alumina. A means is provided for exciting the gas within the tube to create a discharge within a central bore and for conducting heat away from the bore.
In the structure shown in the above cited patents, the means for confining the discharge consists of a plurality of sputter-resistant, coaxially aligned tungsten discs. Each tungsten disc is brazed to a heat conductive copper cup which is, in turn, brazed to the inner wall of the ceramic envelope. In operation, heat from the discharge is transferred by conduction from the discs through the copper cups and through the walls of the ceramic tube to cooling water flowing in a jacket around the ceramic tube.
In the above cited patents, tungsten is utilized for the bore material because it can be brazed to the copper cups, and because it is relatively sputter resistant. The sputter resistance of the bore is important in determining the power output and lifetime of the laser.
In order to produce a commercially viable product, the laser must be capable of operating in the field for at least one thousand hours. A primary limiting factor to operative lifetime is the slow but continuous erosion of the bore defining elements. In use, the bore material is subjected to heat and continuous bombardment by ions, which are accelerated through the wall sheath potential and strike the bore wall. This sputtering process erodes the bore wall and increases the bore diameter until it no longer provides the containment necessary to the lasing process. Accordingly, by selecting materials having high sputter resistance for the bore, lifetime can be increased.
The power output of a laser is intimately related to the lifetime and the sputter resistance of the bore. More particularly, for any given noble gas ion laser structure, if the current and thus the power output are increased, the erosion rate will increase dramatically. Thus, an increase in power is typically accompanied by a corresponding decrease in lifetime such that a more sputter-resistant bore material would be advantageous.
One of the major factors which has prevented the construction of bores with improved sputter resistance is the requirement that the bore material be capable of being readily brazed to the heat conductive cup member. There are presently materials available which are more sputter resistant than tungsten, but are not easily brazed. Some materials are too brittle to withstand the thermally induced stresses associated with a braze joint. Other bore materials are available that could be brazed, however, these materials require braze temperatures or part geometries not compatible with the fabrication of the remainder of the laser tube. It would be highly desirable to develop a bore design which permitted selection of the bore material based on its sputter resistance, independent of its ability to be brazed to the copper cups.
Accordingly, it is an object of the subject invention to provide a new improved conduction cooled graphite bore assembly for an ion laser.
It is a further object of the subject invention to provide a new and improved bore assembly which permits the use of a wide variety of materials for the discharge confining element.
It is another object of the subject invention to provide a new and improved bore assembly which permits the selection of the material forming the discharge confining element without regard to its brazing characteristics.
It is a further object of the subject invention to provide a new and improved bore assembly which permits the discharge confining element to be selected from a group of materials which are highly sputter-resistant.
It is still another object of the subject invention to provide a new and improved bore assembly which facilitates the testing of new bore materials.
It is still a further object of the subject invention to provide a new and improved bore assembly that permits the design of longer lasting lasers.
It is still another object of the subject invention to provide a new and improved bore assembly which will allow a laser to be designed having a greater power output.
It is still a further object of the subject invention to provide a new and improved conduction cooled ion laser with simplified internal parts.